A fiber-optic hydrophone based on adaptive differential weak value measurement technique

Abstract

The application relates to the technical field of quantum precision measurement, in particular to an optical fiber hydrophone based on an adaptive differential weak value measurement technology, which comprises a light-emitting module, a front selection state module, a weak coupling module and a rear selection state module, wherein the light-emitting module is connected with the front selection state module; the output end of the front selection state module is connected with the input end of the weak coupling module through a phase modulation unit and a first polarization division unit; the output end of the weak coupling module is connected with the input end of the rear selection state module through a second polarization division unit; and the output end of the rear selection state module is connected with the phase modulation unit. Through a push-pull probe structure, differential signal processing and an adaptive modulation process, the application realizes high-sensitivity and wide-dynamic-range detection of underwater acoustic signals.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement technology, and in particular to a fiber optic hydrophone based on adaptive differential weak value measurement technology, which is suitable for high-precision detection of underwater acoustic signals in fields such as marine geological exploration, earthquake detection, and military anti-submarine warfare. Background Technology

[0002] Underwater acoustic detection technology, as a crucial means of ocean exploration, is primarily used to capture underwater sound wave signals, playing an irreplaceable role in both civilian and military fields such as marine geology and mineral resource exploration, earthquake detection and research, and anti-submarine warfare. Currently, underwater acoustic detection technology is mainly divided into two categories: traditional piezoelectric hydrophones and fiber optic hydrophones. Traditional piezoelectric hydrophones, based on the piezoelectric effect, convert sound pressure signals into electrical signals. They have the advantages of simple structure and low cost, but their sensitivity is limited by material properties, and they are susceptible to electromagnetic interference in complex marine environments, restricting their application in high-precision detection. Fiber optic hydrophones, on the other hand, utilize optical principles to sense sound pressure signals by detecting changes in light signals. They possess advantages such as resistance to electromagnetic interference, high sensitivity, and excellent environmental adaptability, and are gradually becoming a research hotspot in the field of underwater acoustic detection.

[0003] However, the complexity and diversity of the marine environment pose significant challenges to underwater acoustic detection technology. Environmental factors such as deep-sea high pressure, sudden temperature changes, and salinity fluctuations significantly affect the performance of hydrophones, leading to decreased sensitivity and insufficient stability, which in turn affects the accuracy of detection results. Furthermore, key acoustic signals in the ocean, such as submarine seismic waves, low-frequency sonar from large marine organisms, and long-range underwater communication carrier waves, are mainly concentrated in the low-frequency band below 50Hz. Traditional hydrophones exhibit significantly reduced sensitivity in the low-frequency band, making it difficult to effectively capture weak signals and severely limiting their effectiveness in practical applications. With the increasing demands for marine resource development, environmental monitoring, and military anti-submarine warfare, there is an urgent need to develop new underwater acoustic detection technologies with higher sensitivity, stronger stability, and wider detection range.

[0004] In recent years, the rapid development of quantum measurement technology has provided new solutions for high-precision detection. Quantum measurement technology utilizes the properties of quantum states such as superposition and entanglement to achieve detection accuracy exceeding the limits of classical measurement. Weak value amplification technology based on quantum measurement effectively amplifies weak signals without significantly increasing system noise by coupling them to specific degrees of freedom of quantum states, thereby improving detection sensitivity. However, the effective detection range of standard weak value amplification technology is relatively small, limiting its widespread application in practice. Therefore, this invention, based on standard weak value measurement technology, combines differential detection and adaptive modulation to design an optical fiber hydrophone based on adaptive differential weak value measurement technology, aiming to effectively improve the sensitivity, detection range, and stability of underwater acoustic signal detection. Summary of the Invention

[0005] The purpose of this invention is to address the problems of insufficient sound pressure sensitivity, high equivalent noise pressure, and limited dynamic range in existing technologies by providing an optical fiber hydrophone based on adaptive differential weak value measurement technology. Through a push-pull probe structure, differential signal processing, and adaptive modulation process, it achieves high sensitivity and wide dynamic range underwater acoustic signal detection.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] An optical fiber hydrophone based on adaptive differential weak value measurement technology includes: a light-emitting module, a pre-selection module, a weakly coupled module, and a post-selection module. The light-emitting module and the pre-selection module are connected. The output of the pre-selection module is connected to the input of the weakly coupled module via a phase modulation unit and a first beam splitter. The output of the weakly coupled module is connected to the input of the post-selection module via a second beam splitter. The output of the post-selection module is connected to the phase modulation unit.

[0008] Optionally, the light-emitting module includes a laser for emitting a continuous light beam.

[0009] Optionally, the pre-selection module includes a first half-wave plate and a first polarizer, wherein the first half-wave plate is disposed in the output optical path of the light-emitting module, the incident end of the first polarizer is connected to the first half-wave plate, and the output end of the first polarizer is connected to the phase modulation unit.

[0010] Optionally, the phase modulation unit includes a Soray-Barbigé compensator (SBC), and the first beam splitting unit includes a first polarization beam splitter, a second half-wave plate, a third half-wave plate, a first FC-type fiber optic interface, and a second FC-type fiber optic interface. The Soray-Barbigé compensator (SBC) is connected to the first polarization beam splitter. The first polarization beam splitter is sequentially connected to the second half-wave plate and the first FC-type fiber optic interface as a first beam splitting branch. The first polarization beam splitter is sequentially connected to the third half-wave plate and the second FC-type fiber optic interface as a second beam splitting branch.

[0011] The second beam splitting unit includes a second polarization beam splitter, a fifth half-wave plate, a fourth half-wave plate, a fourth FC-type fiber optic interface, and a third FC-type fiber optic interface. The third FC-type fiber optic interface and the fourth half-wave plate are sequentially connected to and input into the second polarization beam splitter as the third beam splitting branch, and the fourth FC-type fiber optic interface and the fifth half-wave plate are sequentially connected to and input into the second polarization beam splitter as the fourth beam splitting branch.

[0012] Optionally, the weakly coupled module includes a push-pull sensing probe, the input end of which is connected to the first beam splitting branch and the second beam splitting branch respectively, and the output end of which is connected to the third beam splitting branch and the fourth beam splitting branch respectively.

[0013] Optionally, the post-selection module includes a third beam splitting unit, a positive post-selection branch, a negative post-selection branch, and a light intensity contrast verification unit. The third beam splitting unit is connected to the positive post-selection branch and the negative post-selection branch, respectively. The positive post-selection branch and the negative post-selection branch are both connected to the light intensity contrast verification unit, and the light intensity contrast verification unit is connected to the phase modulation unit.

[0014] Optionally, the third beam splitting unit includes a 50:50 beam splitter, the positive back selection branch includes a first quarter-wave plate, a second polarizer, a fifth FC-type fiber interface, and a first optical intensity detector (PD) connected in sequence, and the negative back selection branch includes a second quarter-wave plate, a third polarizer, a sixth FC-type fiber interface, and a second optical intensity detector (PD) connected in sequence.

[0015] The input ends of the first quarter-wave plate and the second quarter-wave plate are both connected to the output end of the 50:50 beam splitter, and the output ends of the first light intensity detector PD and the second light intensity detector PD are both connected to the light intensity contrast verification unit.

[0016] Optionally, the angle between the transmission axis of the second polarizer and the transmission axis of the first polarizer is +φ, and the angle between the transmission axis of the third polarizer and the transmission axis of the first polarizer is -φ.

[0017] The beneficial effects of this invention are as follows:

[0018] The fiber optic hydrophone based on adaptive differential weak value measurement technology provided by this invention improves sound pressure sensitivity by designing a push-pull probe structure and utilizing the opposite deformation of the bi-tube probe. Combined with a differential weak value measurement scheme, differential processing of the selected light intensity after positive and negative selection significantly reduces the equivalent noise pressure and enhances the detection capability of weak acoustic signals. Simultaneously, an adaptive modulation process is introduced, adjusting the selection angle and modulation phase in real time based on the light intensity contrast, solving the problem of traditional hydrophones' difficulty in simultaneously achieving high measurement sensitivity and wide dynamic range. The fiber optic hydrophone based on adaptive differential weak value measurement technology provided by this invention is suitable for high-precision detection of underwater acoustic signals in fields such as marine geological exploration, earthquake detection, and military anti-submarine warfare. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a fiber optic hydrophone structure based on adaptive differential weak value measurement technology according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram illustrating the weak value measurement and signal processing principle of an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of a loosely coupled module structure according to an embodiment of the present invention;

[0023] In this array, 1 is the laser, 2 is the first half-wave plate, 3 is the first polarizer, 4 is the Soray-Barbinée compensator (SBC), 5 is the first polarization beam splitter, 6 is the second half-wave plate, 7 is the third half-wave plate, 8 is the first FC-type fiber optic interface, 9 is the second FC-type fiber optic interface, 10 is the push-pull probe, 11 is the third FC-type fiber optic interface, 12 is the fourth FC-type fiber optic interface, 13 is the fourth half-wave plate, 14 is the fifth half-wave plate, 15 is the second polarization beam splitter, 16 is the 50:50 beam splitter, 17 is the first quarter-wave plate, 18 is the second quarter-wave plate, 19 is the second polarizer, 20 is the third polarizer, 21 is the fifth FC-type fiber optic interface, 22 is the sixth FC-type fiber optic interface, 23 is the first light intensity detector (PD), 24 is the second light intensity detector (PD), and 25 is the computer. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] This embodiment provides a fiber optic hydrophone based on adaptive differential weak value measurement technology, such as... Figure 1As shown, it includes: a light-emitting module, a pre-selection module, a weakly coupled module, and a post-selection module. The light-emitting module and the pre-selection module are connected. The output of the pre-selection module is connected to the input of the weakly coupled module via a phase modulation unit and a first beam splitting unit. The output of the weakly coupled module is connected to the input of the post-selection module via a second beam splitting unit. The output of the post-selection module is connected to the phase modulation unit.

[0027] Specifically, this embodiment improves sound pressure sensitivity by designing a push-pull probe structure and utilizing the opposite deformation of the dual tubes; combined with a differential weak value measurement scheme, the equivalent noise pressure is significantly reduced and the ability to detect weak sound wave signals is enhanced by differential processing of positive and negative selected light intensity; at the same time, an adaptive modulation process is introduced, which adjusts the selected angle and modulation phase in real time according to the light intensity contrast, solving the problem that traditional hydrophones cannot simultaneously achieve high measurement sensitivity and wide dynamic range.

[0028] The fiber optic hydrophone in this embodiment is based on weak measurement theory, which includes three processes: pre-selection, coupling between the system and the pointer, and post-selection. The coupling strength between the system and the pointer in weak measurement theory is relatively weak, represented by a unitary operator. Where U represents the unitary transform operator. For observable measurement of the system, Let g be the operator acting on the pointer, g represent the coupling strength, exp(·) represent the exponential function e, and i represent the imaginary unit. Assume the system's pre-selective state is |ψ i >, perform post-selection on the measurement results, the post-selection state is |ψ f >, with the pre-selected state |ψ i They are almost orthogonal. Therefore, the physical quantity to be measured is related to the weakness value, which can be expressed as:

[0029]

[0030] The larger the weakness value, the higher the amplification factor of the measured physical quantity. As can be seen from equation (1), the more orthogonal the pre-selection and post-selection states are, the smaller the denominator, and the larger the weakness value. Based on the differential weak measurement theory, this invention introduces an adaptive feedback modulation process, using the total post-selection light intensity as a pointer, to achieve high sensitivity while expanding the dynamic range of the fiber optic hydrophone. The principle of weakness value measurement and signal processing in this embodiment is as follows: Figure 2 As shown, the initial state of the pointer is represented as |ψ pi >, the system's pre-selection state is represented as |ψ si Through weak coupling, the pointer and the initial joint state of the system evolve under the action of the evolution operator U, performing positive and negative post-selection on the system. The overall system evolution state is projected onto the post-selected state |ψ. sf± > The selected light intensity I can be obtained from the final state of the pointer. f ± In summary, the light intensity contrast ratio η is calculated.

[0031] Furthermore, the light-emitting module includes a laser 1, which is used to emit a continuous light beam.

[0032] Using continuous light with a center wavelength of λ0 = 1550 nm emitted by laser 1 as the light source, the initial state of the incident light is:

[0033] |ψ pi >=∫dωf(ω)|ω> (2);

[0034] Among them, |ψ pi > represents the initial state vector of the incident light, i.e., the pointer state; |ω> represents the frequency state vector; f(ω) is the Gaussian wavefunction in the frequency domain, expressed as f(ω) = (2πσ) 2 ) -1 / 4 exp[-(ω-ω0) 2 / 4σ 2 ], ω represents the initial light frequency, ω0 represents the center frequency corresponding to the center wavelength of the initial light, σ represents the spectral width of the initial light, and exp[·] represents the natural logarithm.

[0035] Furthermore, the pre-selection module includes a first half-wave plate 2 and a first polarizer 3, wherein the first half-wave plate 2 is disposed in the output optical path of the light-emitting module, the incident end of the first polarizer 3 is connected to the first half-wave plate 2, and the output end of the first polarizer 3 is connected to the phase modulation unit.

[0036] Specifically, in this embodiment, the pre-selection state module is used to obtain the pre-selection state of the incident light. The light beam enters the input end of the first polarizer 3 through the first half-wave plate 2. The output end of the first polarizer 3 is connected to the phase modulation unit. The transmission axis of the first polarizer 3 is placed in the 45° direction to generate 45° linearly polarized light. To obtain higher accuracy, the incident light first passes through the first half-wave plate 2. The intensity of the incident light can be adjusted by adjusting the placement angle of the first half-wave plate 2, and then it passes through the first polarizer 3 for pre-selection. The pre-selection state |ψ si >For:

[0037]

[0038] Where |H> represents the horizontal polarization state of the photon, and |V> represents the vertical polarization state of the photon.

[0039] Therefore, the initial system-pointer joint state |ψ spi >For:

[0040]

[0041] Among them, |ψ pi > represents the initial state vector of the incident light. This represents the direct product.

[0042] Furthermore, the phase modulation unit includes a Solvay-Barbigé compensator SBC4, and the first beam splitting unit includes a first polarization beam splitter 5, a second half-wave plate 6, a third half-wave plate 7, a first FC-type fiber optic interface 8, and a second FC-type fiber optic interface 9. The Solvay-Barbigé compensator SBC4 is connected to the first polarization beam splitter 5. The first polarization beam splitter 5 is sequentially connected to the second half-wave plate 6 and the first FC-type fiber optic interface 8 as a first beam splitting branch. The first polarization beam splitter 5 is sequentially connected to the third half-wave plate 7 and the second FC-type fiber optic interface 9 as a second beam splitting branch.

[0043] The second beam splitting unit includes a second polarization beam splitter 15, a fifth half-wave plate 14, a fourth half-wave plate 13, a fourth FC-type fiber optic interface 12, and a third FC-type fiber optic interface 11. The third FC-type fiber optic interface 11 and the fourth half-wave plate 13 are sequentially connected to and input into the second polarization beam splitter 15 as the third beam splitting branch, and the fourth FC-type fiber optic interface 12 and the fifth half-wave plate 14 are sequentially connected to and input into the second polarization beam splitter 15 as the fourth beam splitting branch.

[0044] The weakly coupled module includes a push-pull sensor probe 10, the input end of which is connected to the first beam splitting branch and the second beam splitting branch respectively, and the output end of which is connected to the third beam splitting branch and the fourth beam splitting branch respectively.

[0045] Specifically, in this embodiment, after the incident light undergoes pre-selection, it is reflected by the first beam splitter unit and enters the weak coupling module. That is, it enters the weak coupling module through the first polarization beam splitter 5, the second half-wave plate 6, the third half-wave plate 7, the first FC-type fiber optic interface 8, and the second FC-type fiber optic interface 9. The weak coupling module includes a push-pull probe 10. For example... Figure 3As shown, the light generated by the pre-selection module is split into two beams, one horizontally polarized and the other vertically polarized, by the first polarization beam splitter 5. The horizontally polarized light passes through the second half-wave plate 6 and is coupled into a polarization-maintaining fiber through the first FC-type fiber interface 8. It is then wound around the inner tube of the probe, transmitted through the fiber, and exits from the third FC-type fiber interface 11. It then passes through the fourth half-wave plate 13 and reaches the second polarization beam splitter 15. The combination of the second half-wave plate 6 and the fourth half-wave plate 13 achieves the polarization-maintaining effect. The vertically polarized light passes through the third half-wave plate 7 and is coupled into another polarization-maintaining fiber through the second FC-type fiber interface 9. It is then wound around the outer tube of the probe, transmitted through the fiber, and exits from the fourth FC-type fiber interface 12. It then passes through the fifth half-wave plate 14 and reaches the second polarization beam splitter 15. The combination of the third half-wave plate 7 and the fifth half-wave plate 14 achieves the polarization-maintaining effect. The two orthogonally polarized beams are then combined and enter the post-selection module.

[0046] When the probe is placed in water to test the sound pressure signal, the inner wall of the inner tube is in contact with the water, and the outer wall is in contact with the air; conversely, the inner wall of the outer tube is in contact with the air, and the outside is filled with water. When the sound pressure p changes, the inner tube is subjected to radial outward pressure and expands outward; at the same time, the outer tube is subjected to radial inward pressure and contracts inward. The opposite deformations of the two tubes form a push-pull structure. At this time, the length of the optical fiber wound on the tube will change slightly, resulting in a small phase shift between horizontal and vertical polarization. It is linearly related to the applied sound pressure p, that is:

[0047]

[0048] Where S is the acoustic pressure sensitivity of the fiber optic hydrophone. Therefore, by measuring the phase shift... The underwater sound pressure p can be obtained indirectly.

[0049] The acoustic pressure sensitivity (S) of a fiber optic hydrophone is an important indicator of its response to acoustic pressure signals. It is defined as the change in optical phase caused by the fiber optic hydrophone probe being subjected to an underwater acoustic pressure signal (p). At the same sound pressure level p, the change in phase of the optical fiber is measured. Traditional fiber optic hydrophone probes typically wind the sensing fiber directly around a single-layer elastic cylinder to detect the sound field. In this embodiment, the push-pull probe 10, due to the opposite deformations of the two tubes, exhibits a different phase shift under the same sound pressure p. It is twice that of the single-tube case. Therefore, according to equation (5), theoretically its sound pressure sensitivity is twice that of the single-tube structure.

[0050] The Hamiltonian H of the interaction between the target system and the measuring pointer can be expressed as:

[0051]

[0052] Where g(t) is the coupling coefficient, Let be the measurement operator of the system, here we let After weak coupling, the state evolution of the entire system is as follows:

[0053]

[0054] in, This is the tiny phase difference generated by the change in sound pressure in the horizontal and vertical polarization directions, which is the phase shift that needs to be measured. Equation (7) is... It is obtained by performing a first-order Taylor approximation under certain conditions.

[0055] Furthermore, the post-selection module includes a third beam splitting unit, a positive post-selection branch, a negative post-selection branch, and a light intensity contrast verification unit. The third beam splitting unit is connected to the positive post-selection branch and the negative post-selection branch, respectively. Both the positive and negative post-selection branches are connected to the light intensity contrast verification unit, which is connected to the phase modulation unit.

[0056] The third beam splitting unit includes a 50:50 beam splitter 16, the positive back selection branch includes a first quarter-wave plate 17, a second polarizer 19, a fifth FC-type fiber optic interface 21, and a first light intensity detector PD23 connected in sequence, and the negative back selection branch includes a second quarter-wave plate 18, a third polarizer 20, a sixth FC-type fiber optic interface 22, and a second light intensity detector PD24 connected in sequence.

[0057] The input terminals of the first quarter-wave plate 17 and the second quarter-wave plate 18 are both connected to the output terminal of the 50:50 beam splitter 16, and the output terminals of the first light intensity detector PD23 and the second light intensity detector PD24 are both connected to the light intensity contrast verification unit.

[0058] The angle between the transmission axis of the second polarizer 19 and the transmission axis of the first polarizer 3 is +φ, and the angle between the transmission axis of the third polarizer 20 and the transmission axis of the first polarizer 3 is -φ.

[0059] Specifically, in this embodiment, the transmitted light beam is split into two beams by a 50:50 beam splitter 16. One beam enters the positive post-selection branch, and the other enters the negative post-selection branch. The positive post-selection branch includes a first quarter-wave plate 17, a second polarizer 19, a fifth FC-type fiber optic interface 21, and a first intensity detector PD23. The first quarter-wave plate 17 is placed at a 45° angle, making the post-selection state almost orthogonal to the pre-selection state, thereby obtaining a larger weakness value. The transmission axis of the second polarizer 19 is at an angle of +φ with the transmission axis of the first polarizer 19, introducing a very small phase shift of +φ. The beam entering the positive post-selection branch passes through the first quarter-wave plate 17 and the second polarizer 19 in sequence to achieve positive post-selection and obtain the positive post-selection state |ψ|. sf + >, positive post-selection state |ψ sf + >For:

[0060]

[0061] Where φ represents the selected angle, i.e. the phase offset, and i represents the imaginary unit.

[0062] The evolved joint state is projected onto the positive post-selection state, and the light intensity I is detected and output by the first light intensity detector PD23. f + I f + It can be represented as:

[0063] I f + =I0|<ψ sf + |Ψ(t)>| 2 ≈I0(sin 2 φ)[1-Im(A w )pS] (9);

[0064] Where I0 is the light intensity value before post-selection. Represents the weak value of an observable, Im(A) w () represents the imaginary part of a weak value. When At that time, the approximation of equation (9) is feasible. It can be seen that after the post-selection, the light intensity and Im(A) are related. w They have a linear relationship.

[0065] The negative post-selection branch includes a second quarter-wave plate 18, a third polarizer 20, a sixth FC-type fiber optic interface 22, and a second intensity detector PD24. The second quarter-wave plate 18 is positioned at 45°. Similarly, in this case, the post-selection state is almost orthogonal to the pre-selection state, resulting in a larger weakness. The transmission axis of the third polarizer 20 is at an angle of -φ with the transmission axis of the first polarizer 3, introducing a very small phase shift -φ. One beam entering the negative post-selection branch passes sequentially through the second quarter-wave plate 18 and the third polarizer 20 to achieve negative post-selection and obtain the negative post-selection state |ψ|. sf - >, Negative post-selection state |ψ sf - >For:

[0066]

[0067] The evolved joint state is projected onto the negative post-selection state, and the second light intensity detector PD24 detects and outputs light intensity I. f - I f - The expression is:

[0068] I f - =I0|<ψ sf - |Ψ(t)>| 2 ≈I0(sin 2 φ)[1+Im(A w )pS] (11);

[0069] Will I f + and I f - The light intensity contrast ratio is obtained by inputting the light intensity contrast ratio into the light intensity contrast ratio verification unit, i.e., computer 25, and performing differential processing. This contrast ratio is denoted by η.

[0070]

[0071] The light intensity contrast can directly reflect the normalized light intensity change caused by the weak amplification of the underwater acoustic signal. The sound pressure p can only be amplified within the range that satisfies the approximate conditions of weak measurement, and the approximation of Equation (12) still guarantees that the linear weak amplification region is satisfied. When the back selection angle is larger, the effective measurement range of the sound pressure is larger, but the measurement sensitivity is lower. Therefore, in order to increase the dynamic measurement range of the fiber optic hydrophone, a certain measurement sensitivity may be sacrificed, which cannot meet the needs of practical applications.

[0072] During measurement, it is essential to ensure that the variation range of underwater sound pressure remains within an effective linear region, which corresponds to the threshold range of light intensity contrast. In this embodiment, the measurement result is considered valid only when the measured light intensity contrast is within the specified threshold range; if the measured light intensity contrast is outside this range, a modulation phase needs to be added.

[0073] In this embodiment, the phase modulation unit employs a Sore-Barbigian compensator (SBC4) to feed back the light intensity contrast measurement results from the post-selection module to the SBC4. After positive and negative post-selection, the corresponding light intensity can be rewritten as:

[0074]

[0075] Where, φ M It is the post-selection angle after modulation. When |pS+β| / 2 << |φ M When | , an approximation is feasible, as this occurs within the linear modulation region. Correspondingly, the light intensity contrast η M for:

[0076]

[0077] Therefore, as long as a suitable modulation phase β is introduced, linear weak amplification of the acoustic signal can always be achieved, thus ensuring that high measurement sensitivity is maintained even when the underwater sound pressure is high, and expanding the dynamic measurement range of the fiber optic hydrophone.

[0078] In this embodiment, after positive and negative post-selection, the first light intensity detector PD23 and the second light intensity detector PD24 are respectively connected to detect the output electrical signal. The measurement is performed at the positive post-selection angle +φ. The voltage value output by the fiber optic hydrophone can be expressed as:

[0079] V1=KΔI1=K(I f + -I f ') (15);

[0080] Where K is the photoelectric conversion efficiency, and I f =I0sin 2 φ represents the absence of sound pressure (i.e., After selecting the light intensity value, I f + This is the output light intensity value under the influence of sound pressure. Similarly, when measured at a negative backselection angle of -φ, the following can be obtained:

[0081] V2=KΔI2=K(I f - -I f ') (16);

[0082] By performing a difference operation on V1 and V2, we can obtain

[0083] ΔV=V1-V2=K(I f + -I f - (17);

[0084] In the standard weak-value measurement scheme, which only measures at +φ or -φ, only V1 or V2 can be measured. Due to the limitation of the fiber optic hydrophone system noise, if the underwater sound pressure is less than the equivalent noise pressure, the effective electrical signal amplitude is very small, meaning V1 or V2 will be drowned out by noise. To reduce the equivalent noise pressure, this embodiment uses a differential weak-value measurement method. By differentiating V1 and V2, some noise can be canceled out, effectively doubling the amplitude of the effective electrical signal. Therefore, ΔV can exceed the noise threshold limit, thus enabling detection and significantly reducing the equivalent noise pressure.

[0085] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An optical fiber hydrophone based on an adaptive differential weak value measurement technique, characterized by, The application relates to a light-emitting module, a front selection state module, a weak coupling module and a rear selection state module. The front selection state module comprises a first half-wave plate (2) and a first polarizer (3), wherein the first half-wave plate (2) is arranged in an output light path of the light-emitting module, the incident end of the first polarizer (3) is butted against the first half-wave plate (2), and the output end of the first polarizer (3) is connected with the phase modulation unit. The phase modulation unit comprises a Sore-Babinet compensator (4), the first light splitting unit comprises a first polarization beam splitter (5), a second half-wave plate (6), a third half-wave plate (7), a first FC-type fiber interface (8) and a second FC-type fiber interface (9), the Sore-Babinet compensator (4) is connected with the first polarization beam splitter (5), the first polarization beam splitter (5) is sequentially connected with the second half-wave plate (6) and the first FC-type fiber interface (8) as a first light splitting branch, and the first polarization beam splitter (5) is sequentially connected with the third half-wave plate (7) and the second FC-type fiber interface (9) as a second light splitting branch; the second light splitting unit comprises a second polarization beam splitter (15), a fifth half-wave plate (14), a fourth half-wave plate (13), a fourth FC-type fiber interface (12) and a third FC-type fiber interface (11), the third FC-type fiber interface (11) and the fourth half-wave plate (13) are sequentially connected and input into the second polarization beam splitter (15) as a third light splitting branch, and the fourth FC-type fiber interface (12) and the fifth half-wave plate (14) are sequentially connected and input into the second polarization beam splitter (15) as a fourth light splitting branch. The weak coupling module comprises a push-pull type sensing probe (10), the input end of the push-pull type sensing probe (10) is connected with the first light splitting branch and the second light splitting branch respectively, and the output end of the push-pull type sensing probe (10) is connected with the third light splitting branch and the fourth light splitting branch respectively. The rear selection state module comprises a third light splitting unit, a positive rear selection branch, a negative rear selection branch and a light intensity contrast verification unit, wherein the third light splitting unit is connected with the positive rear selection branch and the negative rear selection branch respectively, the positive rear selection branch and the negative rear selection branch are both connected with the light intensity contrast verification unit, and the light intensity contrast verification unit is connected with the phase modulation unit. The light-emitting module comprises a laser (1) for emitting a continuous light beam.

2. The fiber-optic hydrophone based on adaptive differential weak value measurement technique of claim 1, wherein, ​ 3. The fiber-optic hydrophone based on adaptive differential weak value measurement technique of claim 1, wherein, The third light splitting unit comprises a 50:50 beam splitter (16), the positive rear selection branch comprises a first quarter wave plate (17), a second polarizer (19), a fifth FC type fiber interface (21) and a first light intensity detector PD (23) connected in sequence, and the negative rear selection branch comprises a second quarter wave plate (18), a third polarizer (20), a sixth FC type fiber interface (22) and a second light intensity detector PD (24) connected in sequence; the input end of the first quarter wave plate (17) and the input end of the second quarter wave plate (18) are connected with the output end of the 50:50 beam splitter (16), and the output end of the first light intensity detector PD (23) and the output end of the second light intensity detector PD (24) are connected with the light intensity contrast verification unit.

4. The fiber-optic hydrophone based on adaptive differential weak value measurement technique of claim 3, wherein, The angle between the pass axis of the second polarizing plate (19) and the pass axis of the first polarizing plate (3) is , and the angle between the pass axis of the third polarizing plate (20) and the pass axis of the first polarizing plate (3) is .

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